Woman with Hyperpigmented Scaling

Specimen Type:

Skin

History:

A 50-year-old woman had a several month history of hyperpigmented adherent scaling in both axillae with minimal itching.

Pathologic Features:

The epidermis has mild hyperplasia with a markedly thickened parakeratotic corneum and with a prominent granular cell layer containing vacuoles. No atypia is seen. There is only a sparse perivascular lymphocytic infiltrate.

Differential Diagnosis:

Acanthosis nigricans

Granular parakeratosis

Psoriasis

Diagnosis:

Granular parakeratosis

Granular parakeratosis was first described in 1991 predominantly affecting the axillae but also may involve other intertriginous areas. Adult women are the most frequently affected. Itching or burning are the most frequent symptoms. The condition is chronic and is not associated with any other disorders. The proposed mechanism is a defect in the transformation of profilaggrin to filaggrin with the resultant failure of degradation of the keratohyalin granules. The histologic features are distinctive as shown in this case with the prominent granular cell layer with vacuoles and the compact thick parakeratotic stratum corneum.